(a) Pneumatic Die Cushion Apparatus
A pneumatic die cushion apparatus is constructed by connecting a pneumatic cylinder that supports a cushion pad and a steel cylinder in which a low pneumatic pressure is accumulated. A pneumatic die cushion apparatus has advantages including convenience and that fact that a surge pressure does not occur since it uses a compressible fluid.
On the other hand, there are disadvantages such as a problem that the size of the apparatus increases due to the need to provide a pit accompanying upsizing of pneumatic cylinders, performance problems such as vibrations upon collision accompanying pressure fluctuations in the compressible fluid or dumping deficiencies, and a problem that additional mechanisms are required in order to overcome a lack of knock-out operation controllability (e.g. an additional mechanism is required when locking a cylinder at the bottom dead center of a press). Accompanying the recent technological advances in the press industry, this may be called an old-style die cushion apparatus.
(b) Oil Hydraulic (Servo) Die Cushion Apparatus
A die cushion apparatus of a press has been proposed that comprises an NC servo valve that obtains a cushioning action by controlling the pressure of cushion cylinders of a cushion pad, and a positional control servo valve that executes pre-acceleration, auxiliary lifting, locking, and lifting of a cushion pad by controlling the pressure oil that is supplied to an upper chamber and a lower chamber of an oil hydraulic cylinder that supports the die cushion pad (Patent Document 1).
This die cushion apparatus can control a surge pressure by pre-accelerating the cushion pad.
(c) Electric (Servo) Type Die Cushion Apparatus
Patent Documents 2 and 3 disclose die cushion apparatuses of presses that control a pressing force for a cushion pad with an electric (servo) motor and screw and nut mechanism, link mechanism, or rack and pinion mechanism.
An advantage mentioned is that control of the pressing force is facilitated since the cushion pad is driven via an electric (servo) motor with good responsivity and (in comparison to hydraulic oil or the like) a mechanism with high rigidity (no loss of responsivity).
(d) Regarding Other Similar and Often Seen Apparatuses
Patent Document 4 discloses a plastic working device according to a hydraulic drive system that, although not a die cushion apparatus, is close thereto with respect to the outward configuration.
This plastic working device according to a hydraulic drive system has a closed combination circuit that is formed by connecting a two-way operation type oil hydraulic cylinder and a two-way discharge type hydraulic pump in a one-to-one condition without mounting a valve therebetween. The plastic working device is configured to drive the oil hydraulic cylinder via the hydraulic pump by driving the hydraulic pump using a direct current servo motor, and to subject a plate material to plastic working using a punch that is driven by the oil hydraulic cylinder.
Patent Document 1: Japanese Patent Application Laid-Open No. 7-24600
Patent Document 2: Japanese Patent Application Laid-Open No. 5-7945
Patent Document 3: Japanese Patent Application Laid-Open No. 6-543
Patent Document 4: Japanese Patent Application Laid-Open No. 10-166199